Signal Processing - November 2017 - 19

Before Assembled

Rod
Mirror

Housing

Optical Beam

Multimode Fiber
Electrical Wire

(a)

Transducer

After Assembled
Ultrasonic Wave
(b)
Torque Coil

(c)

Housing
MMF Tip

Rod Mirror

PURDUE UNIVERSITY

1.6 mm
(d)

Transducer

FIGURE 2. A new catheter probe, developed by researchers at Purdue University, the Indiana University School of Medicine, and the Shanghai Institute
of Optics and Fine Mechanics, can generate three-dimensional images of artery interiors, potentially helping physicians to diagnose plaque on the
verge of rupturing. (a) The main components of the collinear catheter before assembly. (b) The assembled catheter probe. (c) A zoomed-in view of the
catheter tip shows the collinear overlap between optical and ultrasonic waves. (d) The fabricated 1.6-mm catheter probe and the detailed structure of
the catheter tip (inset).

displayed image at video-rate or quasivideo-rate speed requires a number of
advanced signal processing techniques,
including noise shielding," Cao says. "In
our current system we use a preampli-
fication device to boost the signal, data
sectioning to select the effective data we
need, a programmable sampling rate to
reduce the data amount, a median filter
to remove the random noise speckle and
a bandpass filter to remove other noise,"
Cao says. The team also uses a Hilbert
transform to obtain amplitude informa-
tion, polar coordinate projection for fast
coordinate transformation, logarithmic
compression and Tagged Image File For-
mat (TIFF) imaging compression to save
storage space.
The biggest signal processing-relat-
ed challenges facing the researchers are
enabling effective noise filtering, fast
image display, and saving image data to
a hard disk, if necessary. "Our imaging
system can work at a high frame rate,
say, 16 frames per second," Cao says.
"That means in every second a huge
amount of data will be generated and
saved to a computer."
The biggest overall technical challenge
is the contradiction between catheter size

and, hopefully, it can go to clinic in the
and sensitivity. The current diameter of 1
next few years," he adds.
mm is for the bare catheter without a protec-
tive sheath. After integrating the sheath, the
diameter is around 1.6 mm, which is slight-
Peering inside cells
ly large for a coronary application. The
Building on research that won an in-
team is now working to shrink the diameter
ternational team the 2014 Nobel Prize
of the catheter, including a sheath, down to
in Chemistry, Northwestern University
~1 mm to meet the clinical requirement.
engineers say they have developed an
"The further decrease of the catheter size
improved version of a superresolution
will result in both apparent photoacoustic
fluorescence microscopy technique that
and ultrasound loss,
makes it possible to
because both of these
study complex molec-
The biggest signal
waves are reflected by
ular processes in cells.
processing-related
The new optical
a micro-mirror imbed-
challenges facing the
imaging technology-
ded in the catheter,"
spectroscopic photon
Cao says. Another
researchers are enabling
localization micros-
chal--lenge facing the
effective noise filtering,
researchers is the opti-
copy (SPLM)-is sim--
fast image display, and
cal wave scattering that
pler and less expen-
saving image data to a
occurs when the signal
sive than its two pre-
hard disk, if necessary.
travels through blood,
decessors while also
which greatly reduces
offering four times
light intensity and photoacoustic sensitiv-
that resolution, claim the researchers.
ity during in vivo applications.
Like the earlier technologies, SPLM is
"I believe this technology is very
designed to control how fluorescence
promising for future clinical diagnosis
molecules emit, ensuring that no spatially
of human coronary artery disease," Cao
adjacent molecules emit simultaneously.
says, noting that the research is still at a
As a result, each random fluorescence
very early stage. "But we are confident
emission can be considered to very likely
to overcome these technical problems
to come from a single molecule. Based
IEEE SIGNAL PROCESSING MAGAZINE

November 2017

Table of Contents for the Digital Edition of Signal Processing - November 2017